DESCRIPTION: The mechanism that insures accurate distribution of DNA to daughter cells in bacteria is a fundamental, yet poorly understood, process. Study of unit-copy plasmids, such as the P1 prophage, affords an opportunity to dissect the necessary components of this process. The ultimate goal of this research is to define the mechanism the P1 plasmid uses to insure its proper placement in the bacterial cell and to guarantee that each daughter cell will obtain a copy of the plasmid. This process is essential to a full understanding of unit copy plasmid stability and will increase understanding of a critical process in bacterial cell growth. Specifically, the PI proposes to use a genetic screen involving a P1-dependent replicon carrying a lacI gene to identify host mutations affecting P1 partitioning (loss of the plasmid results in blue sectoring of white colonies), and also to use the screen to isolate and characterize selected mutations in the P1-encoded parA and parB genes.